Extreme Heat Events Related To Global Warming

According to a report released this week, extreme heat events will increase unless aggressive actions are rapidly implemented. The Report, issued by the Union of Concerned Scientists, outlines the devastating impacts of increasingly frequent extreme heat events throughout the United States. The Report notes in what is effectively a call to action:

“If we wish to spare people in the United States and around the world the mortal dangers of extreme and relentless heat, there is little time to do so and little room for half measures. We need to employ our most ambitious actions to prevent the rise of extreme heat—to save lives and safeguard the quality of life for today’s children, who will live out their days in the future we’re currently creating.”

The report summarizes the choices the United States faces.

“We have conducted this analysis for three global climate scenarios associated with different levels of global heat- trapping emissions and future warming. These scenarios reflect different levels of action to reduce global emissions, from effectively no action to rapid action. Even the scenario of rapid action to reduce emissions does not spare our communities a future of substantially increased extreme heat. For the greatest odds of securing a safe climate future for ourselves and the ecosystems we all depend on, we would need to take even more aggressive action, in the US and globally, than outlined in any of the scenarios used here. Our challenge is great, but the threat of not meeting it is far greater.”

The Report discusses different levels of extreme heat, including what is referenced as “off the charts”. This is a level of heat that is so high it is literally off the charts currently used to measure such events. What will happen if no action is taken is spelled out as follows:

“A Snapshot of Results

Our results show that, with no action to reduce heat-trapping emissions, by midcentury (2036–2065), the following changes would be likely in the United States, compared with average conditions in 1971–2000:

The average number of days per year with a heat index above 100°F will more than double, while the number of days per year above 105°F will quadruple.

More than one-third of the area of the United States will experience heat conditions once per year, on average, that are so extreme they exceed the current NWS heat index range—that is, they are literally off the charts.

Nearly one-third of the nation’s 481 urban areas with a population of 50,000 people or more will experience an average of 30 or more days per year with a heat index above 105°F, a rise from just three cities historically (El Centro and Indio, California, and Yuma, Arizona).

Assuming no changes in population, the number of people experiencing 30 or more days with a heat index above 105°F in an average year will increase from just under 900,000 to more than 90 million—nearly one-third of the US population.

Countrywide, more than 1,900 people per year have historically been exposed to the equivalent of a week or more of off-the-charts heat conditions; this number is projected to rise to more than 6 million people by mid- century—again, assuming no population changes.

Late in the century (2070–2099), with no action to reduce heat-trapping emissions, the following changes can be expected:

The United States will experience, on average, four times as many days per year with a heat index above 100°F, and nearly eight times as many days per year above 105°F, as it has historically.

At least once per year, on average, more than 60 percent of the United States by area will experience off-the- charts conditions that exceed the NWS heat index range and present mortal danger to people.

More than 60 percent of urban areas in the United States—nearly 300 of 481—will experience an average of 30 or more days with a heat index above 105°F.

The number of people who experience those same conditions—still assuming no population change—will increase to about 180 million people, roughly 60 percent of the population of the contiguous United States.

The number of people exposed to the equivalent of a week or more of off-the-charts heat conditions will rise to roughly 120 million people, more than one-third of the population.

Our results show that failing to reduce heat-trapping emissions would lead to a staggering expansion of dangerous heat. In contrast, aggressive emissions reductions that limit future global warming to 3.6°F (2°C) or less would contain that expansion and spare millions of people in the United States from the threat of relentless summer heat. With these aggressive emissions reductions, the above impacts would, in most cases, be held at or below their midcentury levels and would not grow progressively worse during the second half of the century.”

What our children and grandchildren face, if we take no action, is briefly summarized in the Report as follows: “…in many places around the nation, extreme heat will lead to an increase in deaths or illnesses, disrupt long-standing ways of life, force people to stay indoors to keep cool, and perhaps even drive large numbers of people away from places that become too unpleasant or impractical to live. Outdoor work and play would need to be severely curtailed during the summer months. Power grids could be severely strained. Air and rail travel could be disrupted. Other impacts associated with heat—such as water stress, wildfires, agricultural losses, and ecosystem changes—would become more frequent or severe.”

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